When performing surgical bone interventions such as implanting a prosthesis into a bone, milling to resurface a bone, cutting the bone or drilling of the bone, an accurate recognition of the spatial position of the operative bone is necessary for proper surgery. In traditional surgery, the surgeon recognizes bone position by visual inspection based on his knowledge and experience.
Recently, computer-aided orthopedic surgery and related instruments have been introduced. Using such a system, the planning and execution of the surgery can be aided, especially with the recognition of and tracking of the spatial position of the bone.
For the recognition of the spatial location of the interested bone, several methods have been devised and used. U.S. Pat. No. 6,033,415 describes a method used to recognize or register the location of the bone by digitizing the surface of the bone, i.e., by contacting a probe against the bony surface at a plurality of locations. Once the surface of the bone has been digitized, the acquired data points can be compared against a pre-acquired model of the bone so as to identify the position of the bone in space. With the method of U.S. Pat. No. 6,033,415, the probe can digitize an exposed bony surface, or it can digitize the bony surface by puncturing the skin and contacting the bone. In practice, puncturing of the skin is desirable in some cases so as to reduce the size of the incision made in the patient; but also, it can be challenging to accurately digitize the bony surface through puncturing of the skin and tissue because the “view” is very limited and the tactile feedback is often compromised by the skin, muscle and periosteum. And, also, it has been found that the diameter of the skin puncture is very critical to the amount of pain presented to the patient and the subsequent recovery of the patient after the surgery.
By providing a new method to detect the contact of a thin probe to the bony surface, the digitization of the bone can be done with a minimum amount of invasiveness and it can yield significant patient benefit in the form of accurate and safe surgical results and a fast recovery.